Development mechanism for electrostatic images



Sept. 4, 1956 c. F. CARLSON 2,731,416

DEVELOPMENT MECHANISM FOR ELECTROSTATIC IMAGES .Filed Jan. 2, 1953 3 Sheets-Sheet 1 FIG. I 28 5 INVENTOR.

P 1956 c. F. CARLSON 2,761,416

DEVELOPMENT MECHANISM FOR ELECTROSTATIC IMAGES Filed Jan. 2, 1953 3 Sheets-Sheet 2 F'IGB IN VEN TOR.

p 1956 c. F. CARLSON 2,761,416

DEVELOPMENT MECHANISM FOR ELECTROSTATIC IMAGES Filed Jan. 2, 1953 V 3 Sheets-Sheet 3 35 34 40 I as FIG. 4

INVENTOR.

United States Patent DEVELOPMENT MECHANISM FOR ELECTROSTATIC IMAGES Chester F. Carlson, Fairport, N. 55., assignor to The Battelle Development Corporation, Columbus, ()hio, a corporation of Delaware Application January 2, 1953, Serial No. 329,259

11 Claims. (Cl. 118-51) This invention relates to mechanism for the development of electrostatic images.

This is a continuation-in-part of my co-pending application Serial Number 558,252, filed October 11, 1944 for Graphic Recording, now Patent 2,624,652 granted January 6, 1953.

The development of electrostatic images with powders to produce powder images as practiced in electrophotography, electrostatic powder printing and the like, usually requires that a fine powder be brought into contact with an insulating or partly insulating surface carrying an electrostatic image under controlled conditions so that a dense powder image is deposited on the image without objectionable deposits of powder also being produced on background areas. Development is usually efifected by exposing the surface to a powder clould or by sprinkling or cascading powder or powder developing mixtures over the surface. These methods require elaborate powder transporting and cycling apparatus or else are dependent upon laborious manual operations.

The present invention contemplates development mechanism for developing electrostatic images on flexible sheet material. In its prefered embodiment the mechanism may comprise a pair of spaced rotary members such as wheels or discs around which the band of flexible sheet material is passed toforrn a channel in which powder developer can be tumbled.

In the drawings:

Figure l is an elevation, in section, of an electrographic recording meter;

Figure 2 is a section on the line 22 of Figure 1;

Figure 3 is a vertical section through a development mechanism suitable for higher production rates and capable of handling wider webs of paper or other sheet material;

Figure 4 is a section on the line 44 of Figure 3; and

Figure 5 illustrates the use of the development mechanism with cut sheets.

Referring to Figures 1 and 2 a graphic recording meter is shown for producing powder graphs by the electrophotographic process, as will be clear from my Patent Number 2,624,652 mentioned above. The photoconductive element is in strip form. It may comprise a metal foil strip coated with a layer of photoconductive insulating material, a self-supporting band of photoconductive insulating material, or a paper tape impregnated with such material. For example paper impregnated with anthracene, as described in Carlson Patent 2,297,691, is suitable. This is unwound from a roll 11 and passes over a revolving metaldrum 12 then around a pair of parallel flanged wheels 13 for development and finally between a pair of driven rollers 14 to the outside of the casing 15 of the meter, A driven rotary charging brush 16 applies a frictional electric charge to the band as it starts around drum 12. Positioned above drum 12 is a partition 17 having a narrow slit 18 therein extending along the top edge of the drum. A pair of electric indicating meters 19 and 20 are mounted above the partition with their pointer arms 21 and 22 extending across the slit. An

electric lamp 23 is mounted above the pointers and illuminates the slit casting a narrow band of light across the width of photoconductive tape 10 except where the pointers 21 and 22 produce shadows. The tape is thereby electrically discharged by the light except where the pointer shadows fall. These shadows therefore describe graph curves on the tape as it moves around the drum.

The tape then passes down under the rims of flanged parallel wheels 13 and up again to the driven tension rolls 14. A mass of electroscopic powder 24 rests in the trough formed by tape 10 as it passes under the wheels 13 and is rolled or tumbled by the tape as it moves. A line of powder 28 will adhere to each of the two charged graph curves described by pointers 21 and 22 rendering the record visible. The tape may be printed with suitable indicia and scales to aid in reading the graph.

A roll of moistened paper 25 is mounted in a casing 26 adjacent rolls 14 and the paper is fed between these rolls in contact with the graph surface of tape 1% This paper carries water or other solvent into contact with the powder lines to partially dissolve them and thereby fix them permanently on the tape. Some of the dye will be transferred to paper 25 aiiording a duplicate record, in reverse, of the graph. If alcohol soluble powders such as dyed zein, dyed ethyl cellulose or Vinsol resin are used the paper 25 is moistened with alcohol, alcohol-water mixtures or other suitable organic solvents such as butanol. A pad 27 in casing 26 is also moistened with the solvent. An open container 29 of hygroscopic material such as calcium chloride is mounted in the meter casing to dry the air.

The development mechanism in Figures 1 and 2 is made up of the flanged wheels 13 and their supporting shaft and housing, together with drum 12 which keeps the web under tension as it passes onto the flanged wheels and rollers 14 which apply tension and draw the web along. The electroscopic powder 24 is introduced into the channel of the web after the Web has been threaded around wheels 13, and can be replenished from time to time when necessary. The tumbling of the powder brought about by the travel of the Web around the flanges produces a desirable mixing action while serving its major purpose of applying powder to all parts of the image surface to develop any electrostatic image present.

Figures 3 and 4 show a more elaborate development mechanism suitable for developing electrostatic images of any type on rapidly moving webs of insulating paper, sheet plastic materials, and on flexible electrophotographic webs such as paper coated with a photoconductive insulating material or a photoemissive material.

A pair of spaced discs 30 and 31 are rigidly mounted on an axial hollow shaft 32 which is pivoted for free rotation in bearings 33 mounted in side walls 34 and 35 of the mechanism. The web of sheet insulating material 36 carrying an electrostatic image passes over input feed roller 37 and then is guided under and around the periphery of discs 30 and 31 by a pair of rubber belts 38 and 39 respectively and finally is drawn out of the development mechanism over output feed roller 40. Developer 41, which may comprise a single electroscopic powder, a mixture of two or more powders or a mixture of a fine pigmented powder and a granular carrier material of triboelectrically opposite polarity to the powder, is tumbled in the channel formed by web 36 as it passes around the discs. This brings the developer into intimate contact with the surface of web 36 to develop any electrostatic image carried by the web surface.

Endless rubber belts 33 and 39, after having passed around output feed roller 40 pass downward and under a pair of flanged drive pulleys 42, past tension pulleys 68, and then under and around input feed roller 37 to complete their circuit. Rollers 3'7 and 49 are provided with annular grooves near their ends in which belts 33 and 39 are held as they travel around the rollers and the outer surfaces of the belts and of the rollers thereby provide a substantially smooth surface for supporting the web 35 as it is guided into and out of the mechanism. Drive pulleys 42 are mounted on a shaft 43 which is driven by a motor 44, which may include a gear train, through constant tension clutch 45, which may be a friction clutch or a magnetic fluid clutch. In most cases the web will be drawn off output roller 40 by a motor-driven take-up reel, the web passing through a fusing device to fuse or fix the powder image to the web after development. Consequently the function of motor 44 is primarily to overcome any drag applied to the web by the development mechanism and insure smooth and easy travel of the web through the mechanism. Clutch 45 will therefore usually be set to apply a driving force to drive pulleys 42 equal to the drag produced by the mechanism although in some cases the drive means may also assist in advancing the web through preceeding processing steps, such as unwinding the web from a supply reel and passing it through apparatus which produces or places electrostatic images on the web.

A hopper 46 for catching the developer in event of breakage of web 36 is mounted below the portion of the web which passes around discs 30 and 31 and provided with an outlet chute 47 through which the developer may be emptied. Hopper 46 is insulated from the rest of the mechanism and is provided wtihin its channel with an electrode portion 48 having its inner surface forming a section or are of a cylinder of substantially the same radius as the web which passes around the discs 30 and 31. The hopper is pivoted on insulated mounting screws 49 to be swung toward or away from the under side of the web and its position can be set by tightening a pair of insulated set screws 50 against slotted flanges 51 on the hopper.

Electrode 43 can thus be brought substantially into contact with the back surface of the web throughout the area in which developer is being tumbled, or it can be lowered away from the web by any desired distance up to the maximum of swing permitted by the slotted flanges 51. When the electrode is backed away, as shown in the drawings, it has little effect on the development of the electrostatic images. However, when it is brought close to the back of the web it brings about a realignment of the lines of force, tending to weaken the ability of small charges in background areas to attract powder while at the same time sharpening up line images.

The utility of electrode 48 is greatly increased by applying control potentials to it and for this purpose a potentiometer 52 is provided which is connected across a high voltage battery or other D. C. source 53. The center of the potentiometer is grounded to the. frame of the machine and the sliding tap 54, is connected to electrode 48 so that the potential of the electrode can be varied and can be made positive or negative with respect to the frame. If the fine powder component of the developer carries negative charges, for example, and electrode 48 is brought to a negative potential by adjusting slide 54, the powder is repelled from the background areas and is only attracted to and deposited on the web in areas where a strong positive charge or image overcomes the repulsion caused by the negative electrode. On the other hand, if the image is very weak the potentiometer tap can be adjusted to make the polarity of the electrode aid the image in attracting powder. This may also increase background deposits but in each case the adjustment can be varied to give the best results possible with the electrostatic image which is available.

In order to maintain the desired concentration of pigmented powder in the developer 41 the hollow shaft 32 is provided with a powder feed means and a mixing drum 55 surrounds shaft 32 and is attached to the inside face of disc 30 and has an open end 56 projecting nearly to disc 31. A scoop tube 57 projects out tangentially from the side of drum 55 near the inner face of disc 30 and the end of the scoop tube travels in a circular path which dips it into the developer 41 once each revolution. The open end of tube 57 scoops up a small quantity of developer and the tube carries this into the drum as the drum rotates. The developer tumbles slowly through the drum and falls back into the web channel from open drum end 56.

The powder feed means for adding pigmented toner powder to the powder or powder-carrier mixture 41 comprises a scoop tube 58, similar to tube 57, communicating with the hollow inside of shaft 32 where the shaft projects outside of side wall 34. Powder scoop tube 58 dips into a hopper 59 of powder 64 which is gravity-fed from bin 60. The quantity of powder picked up and conveyed through shaft 32 is regulated by manually set gate 61 on bin 64 which regulates the height of the pile of powder in the hopper 59. The powder is advanced through shaft 32 by spiral vanes 65 until it reaches openings 63 in the wall of the shaft which permit it to fall into tumbling drum 55 and become mixed with that portion of the developer 41 which is being tumbled through the drum.

Circulation and mixing of the developer is usually sutficiently rapid so that the pigmented toner concentration is kept substantially uniform throughout the entire mass and partially depleted developer is brought back to original strength before any difference is noticeable in any portion of the developed web. In some cases a small proportion of carrier may be mixed with the powder 64 in bin 69 to improve its feeding properties. In this event the quantity of carrier in the web channel will gradually increase, but since the quantity of developer is not highly critical this extra amount causes no serious difliculty and can be removed periodically, for instance, when webs are being changed. When one web is finished the developer falls down through chute 47 into a container. After a new web is threaded through the mechanism the preferred quantity of developer is poured into the web channel from above.

The rim of discs 30 and 31 may be of smooth metal, roughened metal or they may be rubber coated. A brush or felt wiper 62 is mounted to rub lightly on each disc rim to remove dust and carrier particles.

Figure 5 illustrates the use of the mechanism of Figures 3 and 4 for developing electrostatic images on cut sheets of flexible material such as paper, plastic, coated metal foil and the like. The operation is exactly the same as with web stock except that in this case the sheets are manually or automatically fed around the discs with the trailing edge of one sheet overlapping the leading edge of the next sheet and so forth. Thus, in Figure 5, the trailing edge of sheet 66 is in front of the leading edge of sheet 67 so that the developer 41 flows smoothly from one sheet to the other without loss. As in the case of the web, the belts 38 and 39, and electrode 48 serve to support and guide the sheets through the mechanism.

The term disc as used in the claims is intended to be construed broadly to include any pivoted circular or eccentric member, wheel, or the like.

While the present invention, as to its object and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed roller rotatable about axes parallel to said disc axis, the axes of rotation of said feed rollers being arranged on opposite sides of and above said disc axis, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input feed roller then under and around the rims of said discs then over saidoutput roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, and a supply of image developing powder in the concave channel formed in said sheet material.

2. A developing mechanism as set forth in claim 1, wherein said input and output feed rollers are each provided with a pair of recessed peripheral grooves, said grooves being aligned respectively with said spaced discs, an endless belt for coactionwith each set of peripheral grooves and discs, each endless belt extending through a groove in the input roller then under and around the rim of the corresponding discs then through the corresponding groove in the output roller, wherebyit underlies the strip of flexible sheet material passing around said rolls and discs.

3. A developing mechanism as set forth in claim 2, wherein at least one of said endless belts is motor driven.

4. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed roller rotatable about axes parallel to said disc axis, the axes of rotation of said feed rollers being arranged on opposite sides of and above said disc axis, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input feed roller then under and around the rims of said discs then over said output roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, a supply of image developing powder in the concave channel formed in said sheet material, an electrode curved to conform to the outer surface of said concave channel and arranged in spaced relation thereto, and a potential source connected to said electrode.

5. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed roller rotatable about axes parallel to said disc axis, the axes of rotation of said. feed rollers being arranged on opposite sides of and above said disc axis, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input feed roller then under and around the rims of said discs then over said output roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, a supply of image developing powder in the concave channel formed in said sheet material, and means for supporting said sheet material through the area in contact with said discs.

6. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed rollerrotatable about axes parallel to said disc axis, the axes of rotation of said feed rollers being arranged on opposite sides of and above said disc axis, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input feed roller then under and around the rims of said discs then over said output roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, a supply of image developing powder in the concave channel formed in said sheet material, and drive means for advancing said sheet material with reference to said discs and rollers.

7. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of parallel sheet material guides, said guides having downwardly convex surfaces, input and output sheet material guides aligned on opposite sides of and above said downwardly convex guides, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input guide then around said downwardly convex guides then over said outputguide, whereby to form an upwardly concave channel in said sheet material as it passes around said guides, a supply of image developing powder in the concave channel formed in said sheet material, and a control electrode curved to conform to a portion of the outer surface of said concave channel, said electrode comprising a conductive layer substantially uniformly spaced from said sheet material.

8. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of parallel sheet material guides, said guides having downwardly convex surfaces, input and outputsheet material guidesaligned on opposite sides of and above said downwardly convex guides,

-a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input guide then around said downwardly convex guides then over said output guide, whereby to form an upwardly concave channel in said sheet material as it passes around said guides, a supply of image developing powder in the concave channel formed in said sheet material, a control electrode curved to conform to a portion of the outer surface of said concave channel, said electrode comprising avconductive layer substantially uniformly spaced from said sheet material and movable toward and away therefrom, and a source of potential connected to said electrode.

9. A developing mechanism for applying developing powder to electrostatic latent imagesformed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed roller rotatable about axes parallel to said disc axis, the axes of rotation of said feed rollers being arranged on opposite sides of and above said disc axis, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged ina path passing over said input feed roller then under and around the rims of said discs then over said output roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, a supply of image developing powder in the concave channel formed in said sheet material, and means for adding additional image developing powder to said powder supply.

10. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed roller rotatable about axes parallel to said disc axis, the axes of rotation of said feed rollers being arranged on opposite sides of and above said disc axis, a strip flexible sheet material having electrostatic latent irnages formed on the upper side thereof, said sheet material being arranged in a path passing over said input feed roller then under and around the rims of said discs then over said output roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, a supply of image developing powder in the concave channel formed in said sheet material, a developing powder mixing chamber arranged between said discs, powder transport means for conveying powder from the powder supply in the concave channel to said mixing chamber, powder feeding means for adding a powder replenishing component to said mixing chamber, and an opening in said mixing chamber for returning replenished developing powder to the powder supply.

11. A developing mechanism for applying developing powder to electrostatic latent images formed on flexible sheet material comprising a pair of spaced coaxial discs pivoted for rotation about a common axis, an input feed roller and an output feed roller rotatable about axes parallel to said disc axis, the axes of rotation of said feed rollers being arranged on opposite sides of and above said disc axis, a strip of flexible sheet material having electrostatic latent images formed on the upper side thereof, said sheet material being arranged in a path passing over said input feed roller then under and around the rims of said discs then over said output roller, whereby to form an upwardly concave channel in said sheet material as it passes around said discs, a supply of image developing powder in the concave channel formed in said sheet material, drive means for advancing said sheet material and thereby rotating said discs, a developing powder mixing chamber coaxially arranged between said discs and rotatable therewith, powder transport means for conveying powder from the powder supply in the concave channel to said mixing chamber, powder feeding means for adding a powder replenishing component to said mixing chamber, and an opening in said mixing chamber for returning replenished developing powder to the powder supply.

References Cited in the file of this patent UNITED STATES PATENTS 558,542 Wheeler Apr. 21, 1896 579,043 Cloudman Mar. 16, 1897 597,074 Squires Jan. 11, 1898 740,879 Lindhard Oct. 6, 1903 1,224,191 Medgyes May 1, 1917 1,661,934 Fatscher et al Mar. 6, 1928 2,143,214 Selenyi Jan. 10, 1939 2,173,032 Wintermute Sept. 12, 1939 2,221,776 Carlson Nov. 19, 1940 2,357,809 Carlson Sept. 12, 1944 2,483,462 Huebner Oct. 4, 1949 2,573,881 Walkup et a1. Nov. 6, 1951 2,586,047 Huebner Feb. 19, 1952 Huebner Mar. 25, 1952 

